Until the fairly recent past it was common practice to use devices known as "aerosol cans" containing a propellant gas of the freon type (chlorofluorocarbon). The use of that propellant is objectionable to ecologists and attempts are being made to do without it. The only replacement propellant gases that have appropriate characteristics are hydrocarbons and these turn out to be dangerous for users.
Proposals have been made in European patent application EP 0 401 060 to use systems that do not include any propellant gas, and that make use of a single-acting pump with a return spring that is generally of the hand operated type and that is actuated rapidly and repeatedly by mechanical means, e.g. 50 or more times a second, thereby obtaining a spray that is projected in a manner that gives the appearance of being the same as when a propellant gas is used. The pump chamber is filled by suction during the return stroke under the action of the return spring. An example of a suitable pump is described in French patents Nos. FR 2 305 241 and FR 2 314 772, and also in U.S. Pat. No. 4,025,046. Another example of a suitable pump is described in European patent application EP 0 330 530 and in U.S. Pat. No. 4,936,492. Those pumps have the advantage of being very cheap since they are generally made of molded plastic and they are mass-produced in the packaging industry for perfumes, cosmetics, and pharmaceuticals.
The pumps used in those applications have pump chambers with a capacity that usually lies in the range of 40 microliters (.mu.l) to 300 .mu.l, and more generally in the range 10 .mu.l to 500 .mu.. Such a pump is mounted by screwing, crimping, or the like onto the neck of a receptacle such as a flask, and it is actuated by a tubular rod that projects vertically and axially from the center thereof. A pusher is mounted on the rod and may include an appropriate spray nozzle depending on the application, with the pusher including an internal channel putting the actuator rod into communication with the nozzle. The pusher serves both to enable thrust to be applied to the pump for emptying its chamber, and to allow the fluid to escape. In addition, if it includes a nozzle, the pusher must hold the nozzle in a manner suitable for spraying. In devices of the kind concerned by the present invention, where the pump and thus the pusher needs to be actuated in rapid repetition, the nozzle or outlet in the pusher is not generally situated on the axis of the pump since it is necessary to apply considerable thrust frequently on the pusher by mechanical or electromechanical means and it is preferable for that to be done on the axis of the pump actuator rod. In general, the pusher is perpendicular to the axis of the pump. The pusher actuator means may advantageously be an electromagnetic device including a fixed winding such as a solenoid and a moving core or plunger which bears against the pusher to actuate the pump when the solenoid is excited. Reciprocating motion can be imparted to the core by rotary means fitted with a crank, a cam, an eccentric, or equivalent means, with or without the use of a return spring. During the downwards motion when the piston compresses the fluid in the chamber in order to expel it, the core moved with the pusher by exerting a driving force thereon against the return spring, after which the core returns under the effect of its own return means while the pusher rises independently under the effect of the return spring of the pump.
The inventor has observed that devices of the kind described above are noisy, subject to vibration, and subject to unwanted variations in the flow rate of the sprayed fluid. These drawbacks are a severe handicap for devices intended for the consumer market, particularly since such devices are in competition with devices that make use of a propellant gas and that are free from such drawbacks.
An object of the present invention is therefore to resolve this technical problem.
The inventor has observed that the problem is related to a lack of synchronization between the pusher and the core due to the possibility of them having different return speeds. Because of this lack of synchronization, the core strikes the pusher while it is still rising, thus giving rise to a more violent shock that generates noise and vibration, and also causing an incomplete quantity of fluid to be expelled since the piston of the pump has not had the time to rise all the way to its rest position for sucking a full dose of fluid into the chamber. In addition, because of the violence of the shock between the core and the pusher, the core may bounce off the pusher, thereby accentuating problems of noise and vibration and also accentuating the phenomenon of loss of synchronization.